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Hexcel and High Modulus have joined forces to prove the benefits of a new carbon reinforcement fabric for high-performance composite marine applications. This new symmetric, relatively light material represents an opportunity to advance the current state of the art in +/- 45° double bias fabrics.
(Published on September 2007 – JEC Magazine #35)
JEAN-CLAUDE DUMOLARD CARBONMULTIAXIALMANAGER FOR COMPOSITE AND INDUSTRIAL REINFORCEMENTS, HEXCEL ALEX SHIMELL, GENERAL MANAGER – EUROPE, HIGH MODULUS
The shear webs of girders in marine composite structures are generally constructed with double bias (+/-45°) carbon or glass fabrics, built up to a specified thickness in order to meet the in-plane shear requirements. During typical construction, multiple layers of material are applied with the same orientation, resulting in an antisymmetric laminate. This can cause distortion on cure, as well as affect the strength performance at high strain levels. With conventional double bias materials, this can only be prevented by rotating the plies through 90° in the mid-plane of the laminate stack.
The new Hexcel material is a three-ply symmetric double bias stitched reinforcement, promoted under the brand name HexForce® NC2 In-ply Symmetric. The reinforcement is internally symmetric – the outer plies are the same weight and have the same fibre orientation (+45°) while the central ply is in the mirrored fibre orientation and has a weight equal to the total of the two outer plies.
High Modulus undertook a comprehensive testing programme to assess this material for use in high-performance yachts. Mechanical testing of in-plane shear, tensile, compressive strength and modulus, and a cure-distortion study were carried out on laminates manufactured from the traditional two-ply (asymmetric) carbon double bias fabric and the three-ply HexForce® NC2 In-ply Symmetric CDB400 fabric. In all areas, the new reinforcement’s performance was superior to the traditional two-ply asymmetric material. For example, the new double bias material is over 10% stronger in in-plane shear and tension than traditional two-ply CDB400.
By using this new fabric in the construction of lightweight yet highly loaded marine structures (e.g. hull girders, bulkheads or booms), there is a reduced risk of premature failure and a reduced risk of shear wrinkling and curling.